JP6849360B2 - Martensitic free-cutting stainless steel with excellent rolling fatigue life characteristics - Google Patents
Martensitic free-cutting stainless steel with excellent rolling fatigue life characteristics Download PDFInfo
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- JP6849360B2 JP6849360B2 JP2016186516A JP2016186516A JP6849360B2 JP 6849360 B2 JP6849360 B2 JP 6849360B2 JP 2016186516 A JP2016186516 A JP 2016186516A JP 2016186516 A JP2016186516 A JP 2016186516A JP 6849360 B2 JP6849360 B2 JP 6849360B2
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- 238000005096 rolling process Methods 0.000 title claims description 33
- 229910001220 stainless steel Inorganic materials 0.000 title claims description 21
- 239000010935 stainless steel Substances 0.000 title claims description 19
- 229910000734 martensite Inorganic materials 0.000 title claims description 12
- 229910000831 Steel Inorganic materials 0.000 claims description 18
- 239000010959 steel Substances 0.000 claims description 18
- 229910052748 manganese Inorganic materials 0.000 claims description 14
- 229910052717 sulfur Inorganic materials 0.000 claims description 12
- 150000003568 thioethers Chemical class 0.000 claims description 10
- 239000000126 substance Substances 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 7
- 229910052802 copper Inorganic materials 0.000 claims description 6
- 229910052750 molybdenum Inorganic materials 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 230000007797 corrosion Effects 0.000 description 20
- 238000005260 corrosion Methods 0.000 description 20
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 8
- 239000000470 constituent Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 229910001105 martensitic stainless steel Inorganic materials 0.000 description 4
- 238000001816 cooling Methods 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 2
- 230000005496 eutectics Effects 0.000 description 2
- 238000009661 fatigue test Methods 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 230000032798 delamination Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
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- Rolling Contact Bearings (AREA)
- Heat Treatment Of Steel (AREA)
Description
本願は、摺動部品や軸受等において転動疲労寿命特性と耐食性が要求される部材で、特に切削加工を受ける部材へ用いられる転動疲労寿命特性に優れたマルテンサイト系快削ステンレス鋼に関する。 The present application relates to martensitic free-cutting stainless steel having excellent rolling fatigue life characteristics, which is used for members to be machined and which is required to have rolling fatigue life characteristics and corrosion resistance in sliding parts, bearings and the like.
従来、転動疲労寿命特性と耐食性が求められる部材にはＳＵＳ４４０Ｃ等の高硬度マルテンサイト系ステンレス鋼が用いられてきた。ＳＵＳ４４０Ｃ等の高硬度マルテンサイト系ステンレス鋼は被削性に乏しく、焼入焼戻し処理を行っていない状態であっても微細な穴加工等が困難である。そこで、被削性向上のために快削元素であるＳを添加したマルテンサイト系快削ステンレス鋼であるＳＵＳ４４０ＦがＪＩＳ Ｇ４３０３に登録されている。ＳＵＳ４４０Ｆは、快削元素であるＳを添加することでステンレス鋼中にＭｎＳを分散させており、切削加工時にＭｎＳが応力集中源となり、亀裂の発生と伝播を助けることで被削性が向上する。しかし、このＭｎＳは耐食性が悪く、被削性を向上させるためにステンレス鋼中のＭｎＳ分散量を増加させると、耐食性が悪化してしまうこととなる。
Conventionally, high-hardness martensitic stainless steel such as SUS440C has been used as a member for which rolling fatigue life characteristics and corrosion resistance are required. High-hardness martensitic stainless steels such as SUS440C have poor machinability, and it is difficult to make fine holes even when quenching and tempering are not performed. Therefore, SUS440F, which is a martensitic free-cutting stainless steel to which S, which is a free-cutting element, is added to improve machinability, is registered in JIS G4303. In SUS440F, MnS is dispersed in stainless steel by adding S, which is a free-cutting element, and MnS becomes a stress concentration source during cutting, and the machinability is improved by assisting the generation and propagation of cracks. .. However, this MnS has poor corrosion resistance, and if the amount of MnS dispersed in the stainless steel is increased in order to improve the machinability, the corrosion resistance will deteriorate.
これに対して、快削元素であるＳの添加を行わずにマルテンサイト系ステンレス鋼中の共晶炭化物の９８％をＣｒ23Ｃ6に制御し、その共晶炭化物の長径を３０μｍ以下、円相当直径を０．３〜１．６μｍ、面積率を２〜７％に制御することで耐食性を悪化させずに被削性を改善させたマルテンサイト系ステンレス鋼が提案されている（例えば、特許文献１参照。）。しかし、炭化物形態を制御するためには、特別な工程追加が必要となるため、コスト増を招き、さらに、ドリル寿命性については考慮されておらず、生産性が低い。 On the other hand, 98% of eutectic carbides in martensitic stainless steel are controlled to Cr 23 C 6 without adding S, which is a free-cutting element, and the major axis of the eutectic carbides is 30 μm or less, circular. Martensitic stainless steels with improved machinability without deteriorating corrosion resistance by controlling the equivalent diameter to 0.3 to 1.6 μm and the area ratio to 2 to 7% have been proposed (for example, patents). See Reference 1.). However, in order to control the carbide morphology, a special process addition is required, which leads to an increase in cost, and further, the drill life is not considered, and the productivity is low.
また、Ｃｒ、Ｍｎ、Ｓの含有量を制御し、硫化物を高耐食化させることで、耐食性と被削性を両立させたマルテンサイト系ステンレス鋼が提案されている（例えば、特許文献２参照。）。しかしながら、この提案では、硫化物の分散状態については言及されておらず、転動疲労寿命特性は考慮されていない。 Further, a martensitic stainless steel having both corrosion resistance and machinability by controlling the contents of Cr, Mn and S and making the sulfide highly corrosion resistant has been proposed (see, for example, Patent Document 2). .). However, this proposal does not mention the dispersed state of sulfides and does not take into account rolling fatigue life characteristics.
本願が解決しようとする課題は、転動疲労寿命特性に優れたマルテンサイト系快削ステンレス鋼を提供することである。 The problem to be solved by the present application is to provide a martensitic free-cutting stainless steel having excellent rolling fatigue life characteristics.
上記の課題を解決するための本発明の手段は、第１の手段では、質量％で、Ｃ：０．５０〜１．２０％、Ｓｉ：０．１０〜０．６０％、Ｍｎ：０．０１〜０．４０％、Ｐ：≦０．０４０％、Ｓ：０．０９〜０．２０％、Ｃｒ：９．００〜１７．００％を含有し、残部がＦｅおよび不可避不純物からなる鋼であり、かつ、上記におけるＭｎとＳはＭｎ／Ｓ≦２．５の関係を有し、さらに、転動面を形成する表面には長径２０μｍ以上の硫化物が１ｍｍ2当り５０〜２５０個分散していることを特徴とする転動疲労寿命特性に優れたマルテンサイト系快削ステンレス鋼である。 The means of the present invention for solving the above problems are, in the first means, in terms of mass%, C: 0.50 to 1.20%, Si: 0.10 to 0.60%, Mn: 0. A steel containing 01 to 0.40%, P: ≤0.040%, S: 0.09 to 0.20%, Cr: 9.00 to 17.00%, and the balance is Fe and unavoidable impurities. In addition, Mn and S in the above have a relationship of Mn / S ≦ 2.5, and 50 to 250 sulfides having a major axis of 20 μm or more are dispersed per 1 mm 2 on the surface forming the rolling surface. It is a martensitic free-cutting stainless steel with excellent rolling fatigue life characteristics.
第２の手段では、第１の手段の化学成分に加えて、質量％で、Ｎｉ：０．０１〜１．００％、Ｍｏ：０．０１〜１．００％、Ｃｕ：０．０１〜１．００％のいずれか１種若しくは２種以上を含有し、残部がＦｅおよび不可避不純物からなる鋼であり、かつ、上記におけるＭｎとＳはＭｎ／Ｓ≦２．５の関係を有し、さらに、転動面を形成する表面には長径２０μｍ以上の硫化物が１ｍｍ2当り５０〜２５０個分散していることを特徴とする転動疲労寿命特性に優れたマルテンサイト系快削ステンレス鋼である。 In the second means, in addition to the chemical components of the first means, in mass%, Ni: 0.01 to 1.00%, Mo: 0.01 to 1.00%, Cu: 0.01 to 1 It is a steel containing .00% of any one or more, the balance being Fe and unavoidable impurities, and Mn and S in the above have a relationship of Mn / S ≦ 2.5, and further. A martensitic free-cutting stainless steel with excellent rolling fatigue life characteristics, characterized in that 50 to 250 sulfides with a major axis of 20 μm or more are dispersed per 1 mm 2 on the surface forming the rolling surface. ..
第３の手段では、第１の手段の化学成分または第２の手段の化学成分に加えて、質量％で、Ｃａ：０．００１〜０．０１０％、Ｍｇ：０．００１〜０．０１０％のいずれか１種若しくは２種を含有し、残部がＦｅおよび不可避不純物からなる鋼であり、かつ、上記におけるＭｎとＳはＭｎ／Ｓ≦２．５の関係を有し、さらに、転動面を形成する表面には長径２０μｍ以上の硫化物が１ｍｍ2当り５０〜２５０個分散していることを特徴とする転動疲労寿命特性に優れたマルテンサイト系快削ステンレス鋼である。 In the third means, in addition to the chemical composition of the first means or the chemical component of the second means, Ca: 0.001 to 0.010%, Mg: 0.001 to 0.010% in mass%. It is a steel containing any one or two of the above, the balance of which is composed of Fe and unavoidable impurities, and Mn and S in the above have a relationship of Mn / S ≦ 2.5, and further, a rolling surface. It is a martensitic free-cutting stainless steel having excellent rolling fatigue life characteristics, characterized in that 50 to 250 sulfides having a major axis of 20 μm or more are dispersed per 1 mm 2 on the surface forming the above.
上記の手段とすることで、摺動部材や軸受等において転動疲労寿命特性と耐食性が要求され、特に切削加工を受ける部材に好適で、転動疲労寿命特性と耐食性に優れたマルテンサイト系快削ステンレス鋼を提供することができる。 By using the above means, rolling fatigue life characteristics and corrosion resistance are required for sliding members, bearings, etc., and it is particularly suitable for members to be cut, and martensitic stainless steel with excellent rolling fatigue life characteristics and corrosion resistance. Machined stainless steel can be provided.
発明を実施するための形態の説明に先立って、本願の各請求項における化学成分の限定理由、および、転動面を形成する表面に存在する長径２０μｍ以上の硫化物個数の限定理由について説明する。 Prior to the description of the embodiment for carrying out the invention, the reason for limiting the chemical composition in each claim of the present application and the reason for limiting the number of sulfides having a major axis of 20 μm or more existing on the surface forming the rolling surface will be described. ..
Ｃ：０．５０〜１．２０％
Ｃは、強度を付与し、転動疲労寿命特性を確保するために必要な元素である。そのためには、Ｃは０．５０％以上とする必要がある。しかしながら、Ｃは１．２０％を超えて含有させると被削性が低下する。そこで、Ｃは０．５０〜１．２０％とする。
C: 0.50 to 1.20%
C is an element necessary for imparting strength and ensuring rolling fatigue life characteristics. For that purpose, C needs to be 0.50% or more. However, if C is contained in an amount of more than 1.20%, the machinability is lowered. Therefore, C is set to 0.50 to 1.20%.
Ｓｉ：０．１０〜０．６０％
Ｓｉは、脱酸元素であり、その効果を得るにはＳｉは０．１０％以上を必要とする。しかしながら、Ｓｉが０．６０％より多いと、素材硬さが上昇し、靱性が低下する。そこで、Ｓｉは０．１０〜０．６０％とする。
Si: 0.10 to 0.60%
Si is a deoxidizing element, and Si requires 0.10% or more to obtain the effect. However, when Si is more than 0.60%, the hardness of the material increases and the toughness decreases. Therefore, Si is set to 0.10 to 0.60%.
Ｍｎ：０．０１〜０．４０％
Ｍｎは、Ｓｉと同様に脱酸元素であり、その効果を得るには、０．１０％以上を必要とする。しかしながら、Ｍｎが０．４０％より多いと、耐食性が低下する。そこで、Ｍｎは０．０１〜０．４０％とする。
Mn: 0.01 to 0.40%
Mn is a deoxidizing element like Si, and 0.10% or more is required to obtain the effect. However, if Mn is more than 0.40%, the corrosion resistance is lowered. Therefore, Mn is set to 0.01 to 0.40%.
Ｐ：≦０．０４０％
Ｐは、不純物元素であり、０．０４０％より多いと熱間加工性を低下させる。そこで、Ｐは０．０４０％以下とする。
P: ≤0.040%
P is an impurity element, and if it is more than 0.040%, the hot workability is lowered. Therefore, P is set to 0.040% or less.
Ｓ：０．０９〜０．２０％
Ｓは、ステンレス鋼の被削性を確保するために必要な元素である。そのためには、Ｓは０．０９％以上とする。しかしながら、Ｓを０．２０％を超えて含有させると熱間加工性が低下する。そこで、Ｓは０．０９〜０．２０％とする。
S: 0.09 to 0.20%
S is an element necessary for ensuring the machinability of stainless steel. For that purpose, S is 0.09% or more. However, if S is contained in an amount of more than 0.20%, the hot workability is lowered. Therefore, S is set to 0.09 to 0.20%.
Ｃｒ：９．００〜１７．００％
Ｃｒは、ステンレス鋼の耐食性を確保するために必要な元素である。そのためには、Ｃｒは９．００％以上とする。しかしながら、Ｃｒを１７．００％を超えて含有させると靱性が低下する。そこで、Ｃｒは９．００〜１７．００％とする。
Cr: 9.00 to 17.00%
Cr is an element necessary for ensuring the corrosion resistance of stainless steel. For that purpose, Cr is set to 9.00% or more. However, if Cr is contained in excess of 17.00%, the toughness decreases. Therefore, Cr is set to 9.00 to 17.00%.
Ｍｎ／Ｓ≦２．５
ＭｎとＳはステンレス鋼中において、硫化物であるＭｎＳを形成し、被削性を改善させる。またＣｒ濃度の高いステンレス鋼中においては、一部のＭｎがＣｒと入れ替わり、（Ｍｎ，Ｃｒ）Ｓを形成する。この（Ｍｎ，Ｃｒ）ＳはＭｎＳと比較して、一般に耐食性が良好である。しかし、硫化物中のＭｎ濃度が高まるに伴って硫化物中のＣｒ濃度が低くなり、それを含有するステンレス鋼の耐食性が悪化することとなる。この耐食性の悪化を回避するためには、鋼中のＭｎとＳの濃度比を制限する必要がある。そこで鋼中のＭｎとＳの質量比はＭｎ／Ｓ≦２．５を満足するものとする。
Mn / S ≤ 2.5
Mn and S form MnS, which is a sulfide, in stainless steel to improve machinability. Further, in stainless steel having a high Cr concentration, some Mn is replaced with Cr to form (Mn, Cr) S. This (Mn, Cr) S generally has better corrosion resistance than MnS. However, as the Mn concentration in the sulfide increases, the Cr concentration in the sulfide decreases, and the corrosion resistance of the stainless steel containing the Cr concentration deteriorates. In order to avoid this deterioration of corrosion resistance, it is necessary to limit the concentration ratio of Mn and S in the steel. Therefore, it is assumed that the mass ratio of Mn and S in the steel satisfies Mn / S ≦ 2.5.
転動面を形成する表面に存在する長径２０μｍ以上の硫化物の個数：１ｍｍ2当り５０〜２５０個
転動疲労環境下ではステンレス鋼と硫化物の界面が応力緩和位置として作用することで、転動疲労による亀裂を生じ難くさせ、また、転動疲労により発生した亀裂が延伸した硫化物と交差する際に硫化物が亀裂先端を鈍化させることで剥離を生じ難くさせるために転動疲労特性は向上する。そのためには、転動面を形成する表面に該硫化物を１ｍｍ2当り５０個以上分散させる必要がある。しかしながら、該硫化物を１ｍｍ2当り２５０個を超えて分散させると熱間加工性が低下する。以上が第１の手段の構成要件である。
Number of sulfides with a major axis of 20 μm or more existing on the surface forming the rolling surface: 50 to 250 per mm 2 In a rolling fatigue environment, the interface between stainless steel and sulfide acts as a stress relaxation position, resulting in rolling. The rolling fatigue characteristics are such that cracks due to dynamic fatigue are less likely to occur, and when the cracks generated by rolling fatigue intersect with the elongated sulfide, the sulfide blunts the crack tip, making it difficult for peeling to occur. improves. For that purpose, it is necessary to disperse 50 or more of the sulfides per 1 mm 2 on the surface forming the rolling surface. However, if the sulfide is dispersed in an amount of more than 250 per 1 mm 2, the hot workability is lowered. The above are the constituent requirements of the first means.
Ｎｉ：０．０１〜１．００％、Ｍｏ：０．０１〜１．００％、Ｃｕ：０．０１〜１．００％のいずれか１種若しくは２種以上を含有
Ｎｉ、Ｍｏ、Ｃｕはそれぞれ耐食性を向上させる元素であり、このためにはＮｉ、Ｍｏ、Ｃｕのいずれか１種若しくは２種以上を０．０１％以上添加させる必要がある。しかしながらこれらの元素において、Ｎｉを１．００％を超えて含有させると被削性が低下し、Ｍｏを１．００％を超えて含有させると、靱性が低下し、Ｃｕを１．００％を超えて含有させると熱間加工性が低下する。そこで、Ｎｉは０．０１〜１．００％、Ｍｏは０．０１〜１．００％、Ｃｕは０．０１〜１．００％のいずれか１種若しくは２種以上の含有とする。以上が第１の手段の構成要件に加えて第２の手段とすべき構成要件である。
Contains one or more of Ni: 0.01 to 1.00%, Mo: 0.01 to 1.00%, Cu: 0.01 to 1.00% Ni, Mo, and Cu are each. It is an element that improves corrosion resistance, and for this purpose, it is necessary to add 0.01% or more of any one or more of Ni, Mo, and Cu. However, among these elements, if Ni is contained in an amount of more than 1.00%, the machinability is lowered, and if Mo is contained in an amount of more than 1.00%, the toughness is lowered and Cu is contained in an amount of 1.00%. If it is contained in excess, the hot workability is lowered. Therefore, Ni is contained in an amount of 0.01 to 1.00%, Mo is contained in an amount of 0.01 to 1.00%, and Cu is contained in an amount of 0.01 to 1.00%, whichever is one or more. The above are the constituent requirements to be the second means in addition to the constituent requirements of the first means.
Ｃａ：０．００１〜０．０１０％、Ｍｇ：０．００１〜０．０１０％のいずれか１種若しくは２種を含有
Ｃａ、Ｍｇはそれぞれ熱間加工性を向上させる元素である。このためには、ＣａとＭｇのいずれか１種若しくは２種を０．００１％以上含有させる必要がある。しかしながら、これらの元素において、０．０１０％を超えて含有させても熱間加工性を向上させる効果は飽和する。そこで、Ｃａは０．００１〜０．０１０％、Ｍｇは０．００１〜０．０１０％のいずれか１種若しくは２種の含有とする。以上が第１の手段の構成要件に加えて第３の手段とすべき構成要件である。
Contains one or two of Ca: 0.001 to 0.010% and Mg: 0.001 to 0.010% Ca and Mg are elements that improve hot workability, respectively. For this purpose, it is necessary to contain 0.001% or more of any one or two of Ca and Mg. However, even if these elements are contained in an amount of more than 0.010%, the effect of improving hot workability is saturated. Therefore, Ca is contained in an amount of 0.001 to 0.010%, and Mg is contained in an amount of 0.001 to 0.010%, whichever is one or two. The above are the constituent requirements to be the third means in addition to the constituent requirements of the first means.
ここで、発明を実施するための形態について説明する。表１に記載の化学成分値からなる発明鋼と比較鋼を１００ｋｇ真空誘導溶解炉で溶製し、鋳造してそれぞれの鋼とした。 Here, a mode for carrying out the invention will be described. The invention steel and the comparative steel having the chemical composition values shown in Table 1 were melted in a 100 kg vacuum induction melting furnace and cast to obtain each steel.
（１）得られた鋼を１１５０℃に加熱し、６０ｍｍ幅×１２ｍｍ厚さに減面率９４％で鍛伸し、次いで、この鍛伸材を１０３０℃から油冷により焼入れし、１５０℃で焼戻し空冷した。これを、外形６０ｍｍ、内径２０ｍｍ、厚さ５．８ｍｍのスラスト型寿命試験片に加工し、試験面をラップ加工により、Ｒａ≦０．０３μｍの表面粗さに仕上げた。 (1) The obtained steel is heated to 1150 ° C. and forged to a thickness of 60 mm width × 12 mm with a surface reduction rate of 94%, and then this forged material is tempered from 1030 ° C. by oil cooling and at 150 ° C. It was tempered and air-cooled. This was processed into a thrust type life test piece having an outer diameter of 60 mm, an inner diameter of 20 mm, and a thickness of 5.8 mm, and the test surface was finished by lapping to have a surface roughness of Ra ≦ 0.03 μm.
（１’）表１の開発鋼のＮｏ．８から得られた鋼を１１５０℃に加熱し、８０ｍｍ幅×５０ｍｍ厚さに減面率６５％で鍛伸し、次いで、この鍛伸材を１０３０℃〜油冷により焼入れし１５０℃で焼戻し空冷した。これを、外形６０ｍｍ、内径２０ｍｍ、厚さ５．８ｍｍのスラスト型転動疲労試験片に加工し、試験面をラップ加工によりＲａ≦０．０３μｍの表面仕上げ粗さに仕上げた。これからなる試験片を比較鋼のＮｏ．８’として表１および表２に示す。 (1') No. of developed steel in Table 1. The steel obtained from No. 8 is heated to 1150 ° C., forged to a thickness of 80 mm width × 50 mm with a surface reduction rate of 65%, and then this forged material is quenched by oil cooling from 1030 ° C. and tempered at 150 ° C. and air-cooled. did. This was processed into a thrust type rolling fatigue test piece having an outer diameter of 60 mm, an inner diameter of 20 mm, and a thickness of 5.8 mm, and the test surface was finished by wrapping to a surface finish roughness of Ra ≦ 0.03 μm. The test piece made of this is the No. 1 of the comparative steel. It is shown in Tables 1 and 2 as 8'.
（２）得られた鋼を１１５０℃に加熱し、８０ｍｍ幅×５０ｍｍ厚さに鍛伸し、次いで、この鍛伸材を８７０℃で焼なまして徐冷した。これを８０ｍｍ幅×５０ｍｍ厚さ×１００ｍｍ長さのドリル寿命試験片に加工した。 (2) The obtained steel was heated to 1150 ° C. and forged to a width of 80 mm × 50 mm in thickness, and then the forged material was annealed at 870 ° C. and slowly cooled. This was processed into a drill life test piece having a width of 80 mm, a thickness of 50 mm, and a length of 100 mm.
（３）得られた鋼を１１５０℃に加熱し、２０ｍｍ径の棒鋼に鍛伸し、次いで、この鍛伸材を１０３０℃から油冷により焼入れし、１５０℃で焼戻し空冷した。これを径１２ｍｍ×２１ｍｍ長さの腐食試験片に加工した。 (3) The obtained steel was heated to 1150 ° C. and forged into a steel bar having a diameter of 20 mm, and then this forged material was quenched by oil cooling from 1030 ° C., tempered at 150 ° C. and air-cooled. This was processed into a corrosion test piece having a diameter of 12 mm × 21 mm.
上記で作製したスラスト型転動疲労試験片に対し、最大接触面圧５．３ＧＰａでスラスト型転動疲労試験機を用いて、剥離までの転動疲労寿命の測定を行い、Ｌ10寿命を測定した。Ｌ10寿命が６．０×１０6サイクル以上を○、６．０×１０6サイクル未満を×として、転動疲労寿命特性を評価した。なお、１０8サイクルで剥離が生じない場合には、剥離なしとして１０8サイクルで試験を終えた。 For the thrust type rolling fatigue test piece prepared above, the rolling fatigue life until peeling is measured using a thrust type rolling fatigue tester at a maximum contact surface pressure of 5.3 GPa, and the L 10 life is measured. did. The rolling fatigue life characteristics were evaluated with L 10 life of 6.0 × 10 6 cycles or more as ◯ and less than 6.0 × 10 6 cycles as ×. The release in 10 8 cycles if not occur, finished test at 108 cycles as no delamination.
ドリル寿命試験は材種ＳＫＨ５０、ドリル径５ｍｍのドリルを用い、周速１９１１ｒｐｍ、送り０．１ｍｍ／ｒｅｖで、穿孔深さ１５ｍｍ、止まり穴のドリル穿孔を乾式にて行い、ドリルが折損するまでの穴数を求めた。ドリル寿命が３０穴以上を○とし、３０穴未満を×として被削性を評価した。なお、１００穴でドリルの折損が生じない場合には、１００穴で試験を終えた。 The drill life test uses a drill of grade SKH50 and a drill diameter of 5 mm, with a peripheral speed of 1911 rpm, a feed of 0.1 mm / rev, a drilling depth of 15 mm, and a dry drill for blind holes until the drill breaks. The number of holes was calculated. The machinability was evaluated with a drill life of 30 holes or more as ◯ and a drill life of less than 30 holes as x. If the drill was not broken at 100 holes, the test was completed at 100 holes.
耐食性は、相対湿度９０％の雰囲気下にて、腐食試験片を２０℃の１．５時間保持と、５０℃の４．５時間保持を２０サイクル繰り返し、腐食試験片の発銹状況を調査し、発銹なしのものを○、発銹ありのものを×として耐食性を評価した。以上の試験結果を表２に示す。 For corrosion resistance, the corrosion test piece was held at 20 ° C for 1.5 hours and held at 50 ° C for 4.5 hours for 20 cycles in an atmosphere with a relative humidity of 90%, and the rusting condition of the corrosion test piece was investigated. Corrosion resistance was evaluated by ◯ for those without rust and × for those with rust. The above test results are shown in Table 2.
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